This invention is in the field of sewing machines, more particularly, it relates to a compact feed system for a sewing machine.
Over a period of years, the household sewing machine has become increasingly more complex and, correspondingly, more capable. The earliest family sewing machines were primarily straight stitch machines, with the ability to perform zigzag stitching coming at a much later time. This ability to produce zigzag stitches was accomplished, in the main, by the use of a cam, and the later of addition of additional cams to produce additional needle patterns was a natural outgrowth of this ability to produce zigzag stitches. With the ability to obtain a blind stitch in a sewing machine, there came the further development of cylinder bed sewing machines, or sewing machines having a flat bed convertible to a cylinder bed, which required compact feed devices to fit into the cylinder bed.
In time, in addition to being able to vary needle position, the sewing machines were also able to depart from a steady feed condition and control feed by cams. Thus, the present day sewing machine is able to vary needle position and to vary feed in order to obtain extremely complicated stitch patterns including those of human or animal figures. At about this same time, or shortly thereafter, the more powerful SCR drive motors were incorporated into sewing machines so as to provide greater operator control over the stitching by control of speed and permit higher speeds to be attained. However, many of these complicated stitch patterns could only be performed at low speeds due to the high inertia of the feed systems and the high feedback of forces from the feed dog to the stitch regulator which caused stitch variations. Still another development in sewing machines made the higher feedback forces more critical, and required the development of another device to lock the feed regulator shaft during the feed portion of the feed cycle in order to prevent shifting of the feed regulator. Thus, in an electronically controlled sewing machine, the linear motor was found to be ideal to shift the feed regulator but offered little resistance to feedback forces from the feed dog.
What is required is a compact feed system having low inertia and which will enable error free implementation of the complicated cam control feed patterns at any sewing machine speed while also providing for low feedback of the feed dog reaction to the stitch regulator. The device which satisfies these requirements, to be useful, must be in compact form to enable its use in a cylinder bed of a sewing machine.